1. Field of the Invention
This invention relates to a workpiece conveyor for conveying a workpiece between presses, and more particularly to a workpiece conveyor which is equipped with a 180.degree. reversing mechanism for a workpiece and can feed the workpiece at a constant pitch.
2. Description of the Prior Art
One example of conventional workpiece conveyors is disclosed in Japanese Utility Model Laid-Open No. 147636/1973 and one example of apparatuses for reversing a workpiece by 180.degree. is disclosed in "Work Transferring Apparatus" of Japanese Utility Model Laid-Open No. 134233/1983.
The workpiece conveyor disclosed in the first reference, i.e. Japanese Utility Model Laid-Open No. 147636/1973 has a construction wherein a carriage equipped with a workpiece receiver is slidably mounted to a carriage guide and reciprocatingly moved by means of a crank and a link mechanism. This conveyor provides the advantages that a stroke which is four times the crank radius can be obtained and the apparatus can be made compact as a whole. On the other hand, the apparatus disclosed in the second reference, i.e. Japanese Utlity Model Laid-Open No. 134233/1983, has a construction wherein a slide guide is disposed between a pair of upper and lower sprockets and a workpiece clamping device is bridged between a chain wound on the sprockets and a slider fitted to the slide guide so that the slider is raised in such a manner as to follow up the rotation of the chain and the workpiece clamping device is reversed by 180.degree. near the raised end of the slider. This apparatus has the advantage that it can be used for both replacement operation and non-replacement operation.
It has been customary in the art to incorporate a so-called "workpiece conveyor" and a reversing mechanism between two presses. If these two apparatuses are incorporated, it becomes necessary to dispose the workpiece conveyors disclosed in Japanese Utility Model Laid-Open No. 147636/1973 at a first station on a press side of a preceding step and at a third station on a press side of a subsequent step and to dispose the workpiece transferring apparatus of Japanese Utility Model Laid-Open No. 134233/1983 at an intermediate second station. In this case, an arm type unloader is disposed on the press side of the preceding step and an arm type loader, on the press side of the subsequent step.
In the workpiece conveyor of the kind described above between a series of presses, however, the workpiece transferring apparatus greatly projects upward and the arms of the loader and unloader interfere with the workpiece transferring apparatus, resulting in the problem that the dimension of the workpiece must be limited or the pitch between the presses must be increased. In such a case, application to existing presses having a small pitch is impossible and the advantages of the workpiece conveyor cannot be fully utilized.
The interference between the arm of the loader-unloader and the workpiece transferring apparatus can be avoided by, for example, providing the carriage with the unloader function. However, unless the unloader has a good timing with replacement operation of the workpiece, the cycle time will be extended uselessly and unless sufficient consideration is paid to arrange the workpiece take-out cycle by the unloader mechanism, strain is likely to occur in the workpiece.
On the other hand, the workpiece transferring apparatus described above is of such a type wherein the workpiece is drastically reversed near the raised end of the slider. Accordingly, if the workpiece is great in size and has low rigidity, strain is likely to occur in the workpiece due to winding pressure, impact at the start and stopping steps, and so forth. Since the transverse width of the workpiece transferring apparatus is fixed so as to correspond to a maximum workpiece, the reversing clamp arm must be elongated to handle a small workpiece, whereby a load increase occurs and durability is decreased, eventually.
Besides the workpiece transferring apparatus described above, the reversing mechanisms include a windmill type, a rack-pinion type, and so forth, but all of them are complicated in construction and cannot easily cope with various shapes and sizes of workpieces.